The pyridine nucleotides NAD and NADP are the most abundant coenzymes in eukaryotic cells, In addition to their well-studied roles in redox reactions, they participate in a variety of non-redox systems, including DNA repair, cell differentiation, Ca2+ mobilization, and phagocytosis. In our study of the NADP-dependent enzyme isocitrate dehydrogenase (IDH) we have synthesized photoreleasable NAD and NADP compounds, with the nicotinamide nitrogen modified with a carboxynitrobenzyl (CNB) caging group. We have characterized these compounds to determine their usefulness in biological systems (since the compounds are identical except for a phosphate group, we will perform flash kinetic analysis on only the caged NADP compound). We have measured the absorption spectrum of the expected aci-nitro intermediate, and used this to determine the quantum efficiency and rate constant for decay of the intermediate. We have also photolyzed the compound in the presence of IDH and monitored the rate of formation of NADPH simultaneously with decay of the aci-nitro species. (These results have been published in Biochemistry 36, 9035 (1997).)